It has been estimated that the prevalence of epilepsy is between 3 and 6 persons per 1000 individuals. For most persons afflicted with epilepsy, pharmacotherapy is the primary form of treatment; antiepileptic agents are also occasionally used in an attempt to improve the behavior of mentally ill or mentally retarded clients. While the physiological side effects of antiepileptic agents are widely acknowledged as problematic, little attention has been paid to the possible behavioral side effects of such drugs. Clinical investigations have yielded conflicting results, and few preclinical studies have appeared. The proposed studies represent an attempt to determine the preclinical behavioral pharmaclogy of five antiepilepsy drugs (phenytoin, valproic acid, phenobarbital, clonazepam, and ethosuximide), each representing a major category of antiepileptic agents. The effects of these drugs will be examined, with pigeons as subject, under conditions where 1) keypecks are maintained under a multiple fixed-ratio fixed-interval schedule of food delivery; 2) keypecks are maintained under a delayed matching-to-sample procedure, and 3) keypecks are maintanined under a repeated acquisition of behavioral chains procedure. The effects of acute and chronic exposure will be examined, as will those of certain drug combinations (phenobarbital and phenytoin, phenobarbital and valproic acid). Obtained results are expected to provide a profile of each drug's behavioral actions (i.e., its effects on learning, memory, and performance under simple schedules of reinforcement), and to allow them to be compared.